Heparin, a sulfonated polysaccharide belonging to the glycosaminoglycans family, is a compound having anticoagulant activity due to its ability to increase the rate with which antithrombin inhibits serine-proteases involved in the blood coagulation cascade.[1-2]
Further to exerting anticoagulant action, heparin partecipates, together with its analogue heparan-sulfate, in several processes, such as cell growth, migration and differentiation. In fact it is involved, both in the free form and bound to proteins, in the angiogenesis and growth of tumoral tissues.[3-7]
Due to its anticoagulant action, heparin is widely used in post-surgical protocols for the prevention of thromboembolism, clotting and thrombi occurring after surgery interventions on the cardiocirculatory system. It is also used in procedures which envisage extracorporeal blood circulation, such as hemodialysis, in therapeutical protocols which involve the use of artificial organs and in organ transplants. In all these cases heparin effects and concentration have to be controlled, and sometimes neutralized, in order to avoid lethal haemorrhages. Therefore, molecules capable of inhibiting heparin or reduce its plasma concentration have interesting therapeutical applications.
At present protamine sulfate is the sole compound used systemically in the treatment of heparin overdosage. Protamine is a low molecular weight protein, extracted from the spermatic cells of some fish, characterized by the presence of a number of arginine residues which render it strongly basic. In a pH range ranging from 6 to 7 protamine, present in cationic form, neutralizes anionic heparin, forming an insoluble and inactive complex. However, sometimes protamine causes side effects, such as hypotension, bradycardia, thrombocytopenia, leucopenia, anaphylactic shock, etc.[8]
Despite continuos efforts to develop novel, more efficient dialysis membranes[9], anticoagulation and neutralization of any anticoagulant excess is still accomplished by heparin-protamine perfusion.
There is therefore the need for molecules that are safer than protamine, especially for extra corporeal devices useful for the prevention of clotting in dialysis circuits, and that allow to reduce to a minimum the risk of haemorrhage in dialysed patients.
It has recently been reported[10-12] that polyphenolic macrocyclic oligomers, commonly referred to as calixarens[12], can be used in the synthesis of polyfunctional mimetic antibodies (U.S. Pat. No. 5,770,380).
WO 01/70930 A2 discloses compounds having a calixaren structure, in particular calix[4]arenes capable of binding growth factors. In particular, each calixarene unit contains arylcarboxylate groups linked to one another at the ortho position to form a macrocycle. Moreover, each calixarene unit bears an alkoxy substituent at the para position to the carboxylic group, which imparts a rigid conformation. Peptidic loops, preferably hexapeptidic loops in which two aminoacids are replaced by a 3-amino-benzamido group, are linked to all or some of the carboxylic groups.